The overall goal of this proposal is to develop differentiation therapy to supplement the treatment regimens for human myeloid leukemia. We will focus on the identification of the most effective analogs (deltanoids) of the physiological form of vitamin D, 1,25-dihydroxyvitamin D3 (1,25D) administered at low concentrations to leukemia cells in culture and study alterations in gene expression and other cellular changes. The deltanoids and 1,25D induce monocytic/macrophage-like differentiation and will also be administered in combination with nontoxic substances currently used as food preservatives or additives, or with potential for such use, to maximize the differentiation activity of of the deltanoids. Further enhancement of the activity of these differentiation agents will be explored by the addition of an anti-inflammatory inhibitor of an intracellular signaling pathway. Established lines of leukemia, as well as samples of leukemic cells freshly obtained from patients, will be used for studies of of cell differentiation. The rationale is provided by previous observation that antioxidants provide a reducing environment and induce expression of genes which complement the differentiation-inducing actions of deltanoid-responsive genes. Insight into differentiation control will be obtained by examination of signaling pathways with particular attention to MAPK pathways and to transcription factors. This will be accomplished by adding pharmacological agents, antisense oligonucleotides, siRNAs, transcription factor decoys, and transfected plasmid constructs to study the molecular consequences of these manipulations , which will be determined by immunoblotting, quantitative RT-PCR, immunoprecipitation, and other standard techniques. Differentiating cells will be monitored by determination of surface markers as well as the activity and the expression of various enzymes. The information obtained in basic studies will be utilized to guide development of a new generation of deltanoids and deltanoid combinations with co- inducers, while translational studies on leukemic cells ex vivo will serve to identify subgroups of myeloid leukemias most suitable for the initiation of clinical trials.